DE 42 35 691 C2 describes a seat in which the seat is to be automatically adapted to the body weight of the particular user. A drawback of seats of this type is the enormous constructional complexity which leads to high costs and to the seat being heavy.
U.S. Pat. No. 6,986,549 B2 discloses a chair with a backrest which reacts to a force acting on it by changing its shape. This backrest is formed by two surfaces which are referred to as skins and have a multiplicity of articulations, mutually opposite articulations of the two skins being connected in each case by individual ribs. On account of its specific design, this backrest tries to adapt itself to every contour and only at its tip has a reaction force which counteracts deformation or movement. Without the ribs connecting them, the so-called skins, which form the surface of the backrest, rather than having any inherent stability, behave like a link chain comprising plates which are each connected by articulations. A chair backrest which is designed in such a way encourages a rounded-back posture and thus definitely does not result in a healthy posture.